The ability to manipulate the world's climate or control the weather for our own benefit is no longer the preserve of science fiction. Technologies are being developed that could provide our only chance to avert catastrophic climate change. Yet these technologies may have unforeseen and potentially devastating consequences. They could even be employed as weapons of war. Despite this there is no agreement on whether, how or under what circumstances they should be employed. It is time for negotiations to begin to draw up a set of international guidelines that govern the future use of geo-engineering. Only then can we be confident that these technologies won't be abused.

Research into the global impact of climate change has led to a better understanding of the complex systems that keep the planet habitable. We are increasingly familiar with the climactic impact of atmospheric aerosols and the role of clouds in reflecting sunlight away from the ground and plankton in absorbing CO2 from the atmosphere. This research has prompted scientists to start developing techniques of climate modification that may have the ability to counteract the effects of a warming planet.

One method that has undergone a series of high-profile trials involves seeding the oceans with iron. Plankton rely on the sun for energy, but like all plants, they require nutrients to live. Adding iron to the seas prompts huge blooms of these microbes, which absorb CO2 from the atmosphere, and when they die some of these plankton fall to the ocean floor, locking away carbon. Just how effective this approach is, though, is a matter of continued debate.

Unlike ocean seeding, another technique – injecting sulphate particles into the upper atmosphere – has a proven track-record. We know it works because in 1991 Mount Pinatubo erupted, releasing 15m tonnes of sulphur dioxide into the stratosphere. There it formed a thick cloud of aerosol particles and within 15 months this had spread across the world, reflecting a significant proportion of the sun's energy back into space. Average global temperatures fell by over 0.5 degrees celsius.

Mankind could mimic this effect in a number of ways. The environmentalist James Lovelock suggests that the necessary cooling could be achieved by filling the tanks of commercial airliners with unrefined sulphur-rich fuels. Others argue that launching sulphur rockets into the stratosphere would be more effective. Whatever the case, the side-effects of these techniques are worrying. Sulphates are known to destroy ozone, while a reduction in sunlight reaching the Earth may impact on plant growth and agricultural yields across the world.

In theory these specific concerns can be avoided. Environmental scientist David Keith believes it is possible to levitate clouds of particles in the atmosphere, positioning them above the ozone layer in the mesosphere, while targeting specific areas where warming is more pronounced – for example the polar regions. Yet even this approach does nothing to limit another impact of increasing atmospheric CO2 levels – ocean acidification. No technology will provide a perfect solution, and legitimate concerns about the practicality of these options persist.

By providing a possible get-out-of-jail card on global warming, geo-engineering may remove the incentive for authorities to curb greenhouse gas emissions. This must not be allowed to happen. Cost is also an issue. Yet despite such misgivings, given the failure of international attempts to reign in CO2 emissions, we rule geo-engineering out at our peril. It may represent a last throw of the dice to avert or delay catastrophic climate change. It could buy us valuable time to end our reliance on fossil fuels.

The debate about geo-engineering has moved out of the shadows. The technology to manipulate the world's climate and weather systems will soon be with us. Like it or not it is here to stay. Beyond the practicalities therefore, it's time to consider the more fundamental questions about its ethics. Should we tamper with the most powerful forces of the natural world? If so who decides what level of warming is acceptable? Also, in a world defined by flux, which adverse weather patterns do we constitute as the norm and which should we strive to prevent?

The ability to control our climate and weather would be the most significant development in the history of mankind. Rather than being subject to the laws of nature, we would instead control them. Despite this there is no international consensus on whether, how, or under what circumstances geo-engineering should ever be employed. It is a matter that requires urgent consideration.

Clearly the world's climate and weather systems are interconnected. What benefits one part of the globe may harm another. An attempt to reduce rainfall in the United States for example, could conceivably lead to droughts in Asia. What's more the possibility of targeted climate modification would have obvious and terrifying consequences if used as a weapon of war.

We need to start thinking about the implications of this technology before it has matured and before the dangers become all too apparent. Discussions must be broached with the aim of drawing up internationally agreed guidelines regarding the potential future use of geo-engineering. Strict conditions must be set governing the circumstances under which such techniques can be employed. Unilateral action must be prohibited and geo-engineering must be outlawed as a form of aggression.

It is possible that climate shifts, as in the past, will be abrupt and catastrophic. If this is the case it is necessary for world authorities to respond quickly and in unison to the threat, and geo-engineering may be a last resort. If successfully negotiated, such guidelines will provide governments with the framework within which to act. If not diplomatic wrangling threatens to erupt as the world burns. Worse still, without a code of ethics enshrined into international law, this technology could herald an era in which weather is no longer regarded as an act of god, but an act of war.